1. Field of the Invention
This invention relates generally to tiltable chairs and in particular a mechanical device particularly useable for the movement and selective locking of a chair.
2. Description of the Prior Art
Tiltable chairs of the prior art generally consist of a seat portion, a back portion, a chair control device and a base portion. The chair control device pivotally connects the base portion of the chair to the seat portion and allows the tilting of a part of the chair in a rearwards and backwards direction when rearward pressure is applied to the back portion of the chair by the person seated in the chair. The chair control is adapted to return the tilting portion when this pressure is released.
These chair control device consist of a fixed frame housing secured to the base portion of the chair, a movable frame portion secured to the tilting portion of the chair (either the seat of the back of the chair) and a biasing means which pivotally connects the fixed frame portion to the resting portion thereby allowing the seat or the back of the chair to be tilted. It is known that the fixed frame housing of the prior art are made up of several components that are affixed together by welding and other means such as bolting the parts together. One area of recurring failure of the existing housings used in tiltable chairs is the extension for the seat locking cam means that is welded onto the housing. Due to the forces of recurring use, the extension often breaks at or near the portion welded to the housing.
The biasing means usually includes an elongated bolt that extends from the interior of the fixed frame portion through the moveable frame portion and marginally beyond. The head of the bolt is placed in the fixed frame portion and a slot or groove is provided in the vertical wall of the fixed frame portion in which the head of the bolt may pivot. The shaft of the bolt extends through the fixed frame portion, through the length of the moveable frame portion and marginally beyond.
A helical compression spring is inserted on that portion of the bolt within the moveable frame portion and the interior end of this spring contacts with the interior vertical wall of the moveable frame portion. A tension control means is inserted on the free end of the bolt. This tension control means usually comprises a pressure plate in contact with the spring, a short sheath about the bolt and affixed to the pressure plate and extending outwards to a hand wheel. The interior of the sheath is screw-threaded corresponding to the screw threading on the end of the bolt.
In order to create tension in the spring, the hand wheel is tightened thereby causing the pressure plate to move inwards contracting the helical spring. Thus, by moving the position of the hand wheel, the amount of tension in the spring may be increased of reduced.
When the user of the chair applies downward pressure to the back portion of the chair, the fixed frame portion moves upward thereby causing the seat and back portions of the chair to tilt rearwards. The tension in the helical spring will cause the device to pivot back on the head of the frame and thus return the tilted portion of the chair to the resting position once the user of the chair releases the rearward pressure.
The chair control device of the prior art generally includes a locking mechanism that includes a release lever and clutch mechanism made up of lamination plates for the purpose of seat angle adjustment as well as for backrest angle adjustment. These lamination packs are clamped between spacers and are locked force closed by a pressure element that can be activated manually by means of the release leaver.
In addition, the chair control device of the art generally includes a gas cylinder for the purpose of controlling the height of the seat of the chair. Generally the gas cylinder is operated by a release leaver by the user of the chair.
The following patents disclose various aspects of the chair control device of the prior art: U.S. Pat. No. 4,013,258 discloses a chair control for tiltable chairs including a simplified and strengthened mechanism with a stronger inner plate of the mechanism; U.S. Pat. No. 4,014,086 discloses a safety feature for chair control devices that includes an additional plate to protect the user in case of a broken bolt of the biasing means; U.S. Pat. No. 4,123,103 discloses a mechanism for a tiltable stenographer's chair including a biasing means made up of a U-shaped bolt with 2 helical springs to eliminate hand wheels; U.S. Pat. No. 4,253,632 discloses a base portion for a tiltable chair including a threaded cylindrical post secured to the chair control device includes an alignment means to align the tubular sleeve in a vertical position in an efficient manner as well as providing a novel bell assembly to facilitate easy adjustment and service of the chair; and U.S. Pat. No. 4,636,004 discloses a seat mounting for a swivel chair that include clutch type locking devices. In addition there exists various design patents showing aspects of tiltable chairs. These design patents include D252,786; D278,961; D246,217; D246,588; and D247,943.